Dispersion strengthening of metals



United States Patent 3,176,386 DISPERSION STRENGTHENING 0F METALSNicholas J. Grant, 10 Leslie Road, Winchester, Mass., and Richard J.Murphy, Belmont, Mass; said Murphy assignor to said Grant No Drawing.Filed Oct. 26, 1961, Ser. No. 147,731 16 Claims. (Cl. 29420.5)

This invention relates to dispersion strengthened metals and, inparticular, to a wet method of producing dispersion strengthened metalscharacterized by improved strength properties at elevated temperatures.

Ever since the discovery of SAP (sintered aluminum powder), much workhas been done in studying the principles of dispersion strengthening andapplying them to new systems. Such metals as Mg, Ag, Cu, Ni, Mo, Be, aswell as Fe, W, Pt, Sn and Cr have been strengthened in this way by avariety of disperse phases. This type of strengthening has been studiedprimarily by means of powder metallurgy techniques, one methodcomprising using metal powder as the matrix-forming material which isblended with finely divided refractory oxide particles, such as A1 0 andthe mix thereafter consolidated and hot worked to the desired shape.Another method of preparation is internal oxidation in which a dilutesolid solution alloy, such as CuAl, in the form of powders or smallchips, is selectively oxidized to produce a dispersion of A1 0 in acopper matrix powder which is thereafter processed in to a wroughtshape. Other methods have included intimately mixing a reducible metaloxide with a refractory oxide, ball milling the mixture, selectivelyreducing the metal oxide and then processing the selectively reduced mixinto a wrought metal shape by consolidation and extrusion.

Attempts were made to use wet mixing techniques in which a solubledecomposable salt dissolved in a solvent is mixed with fine metal powderand the solvent thereafter evaporated and the salt later decomposed to arefractory oxide, but these techniques were difiicult to control and,generally, the final product was inferior to those obtained by the drymethods.

For example, in an attempt to produce nickel dispersion strengthenedwith thoria by the wet method of mixing finely divided carbonyl nickelpowder, for example up to 5 microns in size, with an alcohol solution ofthorium nitrate, an exothermic reaction would usually occur when thenickel was mixed in bulk with the solution, thereby resulting in a harddry residue. After decomposing the salt at 600 C. followed by reductionin dry hydrogen, the material would take on a high degree ofpyrophoricity, and was difficult to handle. Wrought metal productsproduced from powder mixtures prepared in this manner were generallyinferior to dry blending techniques.

We have now discovered a wet method of processing dispersionstrengthened metals whereby superior high temperature strengthproperties are obtained heretofore not obtainable by the dry mixingmethods.

It is the object of this invention to provide a wet method for producingdispersion strengthened metals by powder metallurgy characterized byimproved high temperature strength.

It is also the object of this invention to provide a wet method forproducing a uniform powder mixture of a metal powder and a refractoryoxide from which wrought metal products exhibiting high resistance tocreep at elevated temperature can be produced.

Another object is to provide a dispersion strengthened wrought metalarticle of manufacture.

These and other objects will more clearly appear when taken inconjunction with the disclosure which follows.

Our method comprises providing a finely divided ductile matrix metalpowder, for example ranging up to about ice 44 microns in size andpreferably not exceeding about 10 microns, providing a solution of asoluble decomposable refractory oxide-forming salt, slowly adding thematrix metal powder to the solution while rapidly stirring said solutionto form a homogeneous slurry, to keep the metal particles fromagglomerating together and to insure wetting of each of the particleswith the solution, evaporating said mix under substantially protectiveconditions to form a highly viscous mix such that it is difiicult tostir it any further, confining the highly viscous mix in a container ormold, evaporating the remaining solvent therein to form a dry coherentmass or slug comprising said metal with the salt associated with theparticles thereof, and then subjecting the coherent mass to heating in adry protective atmosphere, e.g., a reducing atmosphere of hydrogen, atan elevated temperature sufficient to decompose the contained salt toform a refractory oxide finely and uniformly dispersed therethrough. Thecoherent mass in this form is generally free from blow holes, piping orsevere local porosity and can be consolidated to a compact and thenextruded under protective conditions to a wrought shape characterized byimproved high temperature strength.

In producing the wet mix, we slowly add the metal powder to the saltsolution while rapidly stirring to form the slurry. The rate of stirringshould be at least sufficient to avoid isolated heavy concentration ofthe solution in the wet mix so as to inhibit a high rise of temperaturewhich otherwise occurs exothermically when the mass is not homogeneouslymixed. The rapid rate of stirring may go as high as 20,000 r.p.m. andrange from about 5,000 to 20,000 rpm.

In one embodiment of our invention, we are able to achieve markedly highresistance to rupture at high stresses at up to about 815 C. and higherfor wrought nickel by utilizing thoria as the disperse phase decomposedfrom thorium nitrate.

While, as stated herein, the particle size may range up to about 44microns and more desirably up to 10 microns, we prefer it not exceedabout 5 microns, and more preferably, range from about 0.1 to 1 or 2microns.

The metal powder may be ductile metal having a melting point above 250but usually may exceed 650 C. Such metals may include the copper groupmetals Cu, Ag, Au and alloys based on these metals; the metals Pb, Znand alloys based on these metals; the iron group metals Fe, Ni, Co andalloys, particularly heat resisting alloys based on these metals; theprecious metals Pt, Pd, Ru, Rh, Ir, Re and alloys of these metals witheach other and other metals; certain of the refractory metals W, Cr. Mo,Ti, Zr, V, Cb, Ta and alloys thereof.

Examples of such copper-group alloys are: 90% copper and 10% nickel,copper and 20% nickel; 70% copper and 30% nickel; 70% copper and 30%gold; 65% copper, 30% gold and 5% nickel; silver and 10% copper; up to15% nickel and the balance silver; 70% gold and the balance palladium,69% gold, 25% silver and 6% platinum, and similar alloys.

Examples of iron group alloys include: steels, 64% iron and 36% nickel;31% nickel, 4 to 6% cobalt, and the balance iron; 54% iron and 46%nickel; 90% iron and 10% molybdenum or tungsten; 90% nickel and 10%molybdenum or tungsten.

Heat resisting alloys based on one or more of the iron group metalsnickel, iron and cobalt may also be dispersion strengthened.

With respect to precious metal alloys, the following are examples:platinum-rhodium alloys containing up to 50% rhodium; platinum-iridiumalloys containing up to 30% iridium; platinum-nickel containing up to 6or 10% nickel; platinum-palladium-ruthenium containing 77% 3 toplatinum, 13 to 88% palladium, and 10 to 2% ruthenium; alloys ofpalladium-ruthenium containing up to 8% ruthenium; 60% palladium and 40%silver; 90% platinum and 10% rhenium, and others.

With regard to the decomposable refractory oxide- :forming salts, weprefer those salts which are soluble in non-residue leaving solvents,such as Water, or alcohol and other organic solvents, and which saltsdecompose to a refractory oxide whose negative free energy of formationis at least about 100,000 calories per gram atom of oxygen at about C.and, more preferably, at least about 120,000 calories.

The solvent should be one which evaporates below the decompositiontemperature of the salt and does not leave aresidue.

We prefer that the soluble salt be one whose decomposition temperaturedoes not exceed the melting point of the metal and preferably does notexceed 550 C. More preferably, it is desired the decomposition does notexceed about 375 C. Examples of soluble refractory oxideforming saltswhich decompose to form dispersions of refractory oxide are Th(NO -4H O;Al(NO -9H O;

etc. Certain of the chloride salts may be employed provided theprevailing conditions are such as to favor formation of oxides. Thus,the salts may comprise nitrates, oxalates, acetates, chlorides and thelike. The foregoing salts are at least to some extent soluble in water,alcohol or both. The refractory oxides formed by the decomposition ofthese salts have negative free energy of formation of at least about100,000 calories per gram atom of oxygen at about 25 C.

We prefer to use thorium nitrate as the source of the refractory oxideThO as We have been able to realize exceptionally high strengthproperties with it. In addition, we find thorium nitrate easy to workwith because of its high solubility in alcohol.

In order to insure optimum strength properties in the final product, weprefer that the metal powder be as fine as possible. We find the powderto be satisfactory for our purposes when it has been reduced to yield ahigh specific surface which is generally indicated when the powderexhibits pyrophoricity on exposure to an oxygencontaining atmosphere.However, in order to utilize the advantages of such a powder, particularcare must be taken to handle the powder under substantially inertenvironment or conditions. When powder is being reduced for our purposesto sizes below 3 microns say, for example, in an attrition mill, weprefer the grinding be carried out in alcohol or other suitable liquidin a controlled atmosphere, such as argon or other inert gas. After thepowder has been suitably ground, it is washed and dried in an inert orprotective environment, e.g., argon, and retained protected for wetmixing with the dissolved refractory oxide-forming salt.

Of course, other means may be used to insure an inert or protectiveenvironment, such as a vacuum, or a liquid medium. A still furthermethod would be to stabilize the finely ground metal powder duringgrinding. For example, during wet grinding, suflicient oxygen might bebled into the mill atmosphere so that any oxidation which takes place inthe mill environment is controlled in accordance with the prevailingoxygen partial pressure. Thus, the finely ground metal powder would bestabilized to the extent that its pyrophoricity would be sufiicientlyinhibited to render the powder easier to handle in subsequentoperational steps. Thus, the terms inert environment, protectiveenvironment, inert conditions and similar terms are meant to cover thosemeans of protecting the powder to avoid as far as possible from itmarkedly undergoing spontaneous ignition.

In order to obtain a better understanding of the invention, thefollowing examples are given:

EXAMPLE 1 In producing Alloy No. 1, carbonyl nickel powder having a sizeranging from about 2 to 5 microns was employed. The nickel powderamounted to 1000 parts by weight and was divided into 5 equal portionsof 200 parts each. Five portions of thorium nitrate were provided, eachcomprising 45.2 parts by weight. The total amount of thorium saltcorresponded to an oxide loading in the neighborhood of about 9 volumepercent. Each portion of the salt was dissolved in about 118 parts byweight of methyl alcohol and to each solution was slowly added 200 partsby weight of the carbonyl nickel powder and the solution stirred in aWaring Blendor at about 15,000 rpm. for about 5 minutes to form aslurry. The five mixed batches were then combined and agitated whilebeing heated at a temperature of about 60 C. until the slurry thickenedby evaporation and became so viscous that it could no longer be stirred.The highly viscous slurry was then confined in a glass mold and theremaining solvent evaporated at C. and the thorium nitrate decomposed indry hydrogen for 4 hours at 600 C.

A hard, solid residue remained which was ball-milled in a stainlesssteel ball mill for about one-half hour followed by a reductiontreatment at 600 C. in dry hydrogen. The powder was then vacuumcompacted in a rubber stoppered rubber sleeve within a perforated openend metal tube and then hydrostatically pressed at 25,000 psi. Afterevacuating air from the assembly, the compact inside the rubber sleevewas hydrostatically pressed at the aforementioned pressure. The pressedbillet was then sintered in dry hydrogen at 950 C. for 8 hours. It wassealed in a mild steel can and heated for one hour at about 1093" C. andextruded in a 300 ton press at a ratio of 25 to 1. The extruded productwas then prepared for testing to be described later.

EXAMPLE 2 Alloy No. 2 was prepared similarly to Example 1 except thatafter the slurry was evaporated to a point of high viscosity wherein itwould no longer be mixed by stirring, it was poured into a mold having adimension corresponding substantially to that of an extrusion can. Themold was lined with a removable flexible rubber or plastic sleeve closedat one end. The mold was adapted to be evacuated while being heated in ahot water bath at a temperature of about 60 C. During evacuation, themold was vibrated until substantially all of the solvent had beenremoved and until the slurry had hardened in the mold in the form of aslug. Thereafter, the hardened slug was removed from the rubber sleeveand cut trans versely in half and the halves heated to 100 C. in argonfor 1 hour and thereafter decomposed in dry hydrogen at 600 C. and thenreduced in hydrogen at the same temperature for about 5 hours. Theunsintered slugs were then cold compacted to a density of about 60%theoretical in a mild steel extrusion can 2 inches inside diameter by 3inches long and then extruded at 1093 C. at an extrusion ratio of about25/1 as aforementioned. The oxide loading was in the neighborhood ofabout 9 volume percent.

In a comparison example, an alloy designated as 3X was produced bydissolving 142 grams of thorium nitrate in sufiicient methyl alcohol towet completely 500 grams of carbonyl nickel powder of about 2 to 5microns in size, the mixture being stirred by hand. When all the nickelwas added, an exothermic reaction occurred in which all of the alcoholwas in some way reacted so that the residue was dry. After decomposingthe residue in argon at 600 C. for 2 hours to form thoria, it wasreduced in dry hydrogen at 600 C. and exhibited pyrophoricity and tendedtowards oxidation. After a second reduction treatment, the powder wasvacuum compacted, hydrostatically pressed into a billet at 75,000 psi,followed by reduction in hydrogen at 600 C. and then sintered in dryhydrogen at 900 C. for 24 hours. Following this, the resulting compactwas vacuumed sealed in a mild steel extrusion can and extruded under thesame conditions as Alloy Nos. 1 and 2 except at an extrusion ratio of34/ 1. The oxide loading was in the neighborhood of about 11 volumepercent.

Room temperature properties were obtained on Alloy Nos. 1 and 2 andstress-rupture properties at elevated temperatures obtained for AlloyNos. 1, 2 and 3X. The specimens had a gauge length of one inch and adiameter of 0.16 inch.

For comparison purposes, nickel dispersion strengthened with 9 volumepercent A1 0 No. A, was also tested. This alloy was produced by drymixing five micron nickel powder and 0.018 micron A1 0 powder,compressing the mixture into a slug and extruded the slug as in Examples1 and 2 into a Wrought metal shape.

Also, for comparison purposes, a nickel-thon'a result, No. B, isincluded produced by wet mixing NiO (0.2 to 2 microns) and thoriumnitrate, decomposing the nitrate, selectively reducing the nickel oxideand then compressing and extruding the mixture encased in a mild steelcan. The room temperature properties (excluding No. 3X) are compared asfollows:

It is apparent from Table 1 that Alloys 1 and 2 are markedly superior inphysical properties to Alloys A and B.

A comparison of the stress-rupture characteristics at 815 C. is given asfollows in Table 2:

Table 2 Stress-Rupture at 815 C. (p.s.i.)

A110 No.

y 1 Hr. 10 Hr. 100 Hr.

Stress Stress Stress It is likewise apparent that Alloy Nos. 1 and 2 areconsiderably superior to 3X, A and B at 815 C. Alloy No. 3X illustratesthe importance of processing variables on the properties of the finalproduct. Thus, in the case of 3X where an exothermic reaction occurredduring powder mixing, it adversely affected the final properties of thealloy. On the other hand, where particular care was taken during theinitial stages of wet mixing to produce a viscous slurry which couldthereafter be handled easily in producing a hard slug prior tosubsequent heating, optimum room and high temperature properties wereobtained. The properties were even markedly superior to Alloy B preparedfrom NiO and thorium nitrate.

6 Additional comparison tests at about 982 C. (1800 F.) are given inTable 3.

Table 3 Stress-Rupture at 982 0.

Alloy N0.

1 Hr. 10 Hr. Hr.

Stress, p.s.i. Stress, p.s.1. Stress, p.s.1.

It will be noted that as the temperature increases, the comparativestrength factor for Alloys 1 and 2 appears to increase over No. 3X andNo. A.

It is apparent from the foregoing that the wet method of using thoriumnitrate in conjunction with very fine metal powders enables obtaininghigh strength in the resulting wrought product. As is also apparent fromthe inferior results obtained on Alloy 3X and Alloy B, the wet method isvery sensitive to process variables. Since the aim of this method is tocoat each nickel particle with a thin layer of refractory oxide, it isimportant that, during the formulation of the mix, the mixing beeffected through rapid stirring, such as is achieved by a WaringBlendor, in order to insure breaking down of agglomerates of metalpowder. The adverse afiect of the mixing employed in producing 3X wasapparent from a microstructure obtained of Alloy 3X which showed acoarser disperse phase than that obtained for Alloys 1 and 2. The rapidstirring is also important in that it inhibits as far as possible theexothermic reaction which otherwise occurs in bulk mixing.

In applying the inventive concept to the dispersion strengthening ofcopper or copper group metals or alloys with alumina, the procedure issimilar. As in the case of nickel powder, copper powder in theneighborhood of about five microns is slowly added to an alcoholsolution of aluminum nitrate while rapidly stirring the same. After allthe copper has been added to form a slurry, the stirring is continuedand the slurry gently heated at about 60 C. until the slurry thickens byevaporation and increases in viscosity so that it no longer can be mixedby stirring. The highly viscous slurry is then confined in a mold anddried at about 100 C. to form a coherent solid residue which isthereafter heated in dry hydrogen at 600 C. to decompose the aluminumnitrate. The copper powder slug which remains from this treatment isthen prepared for extrusion as described above in Example 2, followed byencasing the copper in a copper can and extruding it at a temperature ofabout 760 C. Copper dispersion strengthened in this manner likewiseexhibits improved high temperature strength.

In the production of platinum or platinum alloys dispersion strengthenedwith a refractory oxide, such as BeO, finely divided platinum in thesize range of about 1 to 5 microns is slowly added to a solution ofberyllium nitrate dissolved in alcohol and rapidly stirred as aforesaidto form a slurry which is thereafter thickened by evaporation and pouredinto a mold and thereafter dried to form a slug. The slug is decomposedby heating it to a temperature of about 205 C. in dry hydrogen. Thedecomposed platinum slug is then reduced in dry hydrogen at about 250C., canned in a stainless steel can and extruded at about 1000 C. at anextrusion ratio of about 25 to 1. Platinum dispersion strengthened inthis manner exhibits improved high temperature strength, e.g., at 1100C., superior to similar compositions produced by dry mixing. Platinumdispersion strengthened with 8 volume percent of thoria in accordancewith the invention is capable of exhibiting a 100 hour stress of 3200psi. at 1100 C.

We have found that by this Wet method of mixing, we

are able to disperse refractory oxide in the sub-micron range of up toabout 0.5, and more preferably from about .01 to 0.3 micron, whether theoxide is ThO A1 BeO, ZrO the rare earth metal oxides CeO La O Y O andthe like, MgO, CaO, etc.

The amount of decomposable salt employed should be sufiicient to yieldan oxide loading in the product ranging from about 2% to 25 volumepercent and, more preferably, from about 4 to 12 volume percent.

While it has been indicated that the refractory oxide referred to shouldhave a negative free energy of formation of at least about 100,000calories per gram atom of oxygen at about 25 C. and, preferably 120,000calories,-

it is also preferred that the melting point of such refractory oxide beat least about 1600 C.

Generally speaking, the extrusion ratio employed in producing thewrought metal product may range from about to 1 to 50 to 1, and morepreferably from about to 1 to to 1.

Although the present invention has been described in conjunction withpreferred embodiments, it is to be understood that modifications andvariations may be resorted to without departing from the spirit andscope of the invention as those skilled in the art will readilyunderstand. Such modifications and variations are considered to bewithin the purview and scope of the invention and the appended claims.

What is claimed is:

l. A wet method for producing a homogeneous metalcontaining mixture foruse in the production of dispersion strengthened wrought ductile metalsof melting point above 250 C. having a uniform dispersion therethroughof a refractory oxide phase whose negative free energy of formation isat least about 100,000 calories per gram atom of oxygen at about 25 C.which comprises, providing a solution of a soluble decomposablerefractory oxide-forming salt with a non-residue leaving solvent, saidsalt being one which decomposes on heating to a refractory oxide whosenegative free energy of formation is at least about 100,000 calories pergram atom of oxygen at about 25 C., slowly adding said finely dividedductile matrix metal powder of melting point above 250 C. to saidsolution while rapidly stirring and evaporating said solution to producea highly viscous slurry which tends to resist further stirring,confining the highly viscous slurry in a mold, evaporating substantiallyall of the solvent therefrom to form a dry solid residue comprising saidductile metal with said salt associated with the particles thereof, andsubjecting said residue to heating in a dry reducing atmosphere at anelevated temperature sufficient to decompose said salt to form arefractory oxide finely dispersed therethrough.

2. The method of claim 1 wherein the amount of refractory oxide-formingsalt wet mixed with the metal powder corresponds to about 2% to 25% byvolume of its corresponding refractory oxide taken on the dry basis ofthe metal powder mixture.

3. The method of claim 2 wherein the salt is a thorium salt whichdecomposes to thoria.

4. The method of claim 3 wherein the thorium salt is thorium nitrate,and wherein the amount of thorium nitrate present corresponds to about4% to 12% by volume of thoria taken on the dry basis of the metal powdermixture.

5. The method of claim 4 wherein the particle size of the finely dividedmetal powder range up to about 10 microns.

6. A wet method for producing dispersion strengthened wrought ductilemetals of melting point above 250 C. having a uniform dispersiontherethrough of a refractory oxide whose negative free energy offormation is at least about 100,000 calories per gram atom of oxygen atabout 25 C. which comprises, providing a solution of a solubledecomposable refractory oxide-forming salt with a non-residue leavingsolvent, said salt being one which decomposes on heating to a refractoryoxide whose negative free energy of formation is at least about 100,000calories per gram atom of oxygen at about 25 C., slowly adding saidfinely divided ductile matrix metal powder of melting point above 250 C.to said solution while rapidly stirring and evaporating said solution toproduce a highly viscous slurry which tends to resist further stirring,confining the highly viscous mix in a mold, evaporating substantiallyall of the solvent therefrom to form a dry solid residue comprising saidductile metal with said salt associated with the particles thereof,subjecting said residue to heating in a dry reducing atmosphere at anelevated temperature sufiicient to decompose said salt to form arefractory oxide finely dispersed therethrough, consolidating saidresidue into a hot workable compact, and hot working said compact into awrought metal shape.

7. The method of claim 6 wherein the amount of refractory oxide-formingsalt wet mixed with the metal powder corresponds to about 2% to 25% byvolume of its corresponding refractory oxide taken on the dry basis ofthe metal powder mixture.

8. The method of claim 7 wherein the oxygen-containing salt is a thoriumsalt which decomposes to thoria.

9. The method of claim 8 wherein the thorium salt is thorium nitrate,and wherein the amount of thorium nitrate present corresponds to about4% to 12% by volume of thoria taken on the dry basis of the metal powdermixture.

10. The method of claim 9 wherein the particle size of the finelydivided metal powder ranges up to about 10 microns.

11. A Wet method for producing a homogeneous metalcontaining mixture foruse in the production of dispersion strengthened wrought ductile metalsselected from the group consisting of nickel and nickel-base alloyshaving a uniform dispersion therethrough of a refractory oxide phasewhose negative free energy of formation is at least about 100,000calories per gram atom of oxygen at about 25 C. which comprises,providing a solution of a soluble decomposable oxygen-containingrefractory oxide-forming salt with a non-residue leaving solvent, saidsalt being one which decomposes on heating to a refractory oxide whosenegative free energy of formation is at least about 100,000 calories pergram atom of oxygen at about 25 C., slowly adding said finely dividedductile matrix metal powder selected from said group consisting of saidnickel and nickel-base alloys to said solution while rapidly stirringand evaporating said solution to produce a highly viscous slurry whichtends to resist further stirring, confining the highly viscous slurry ina mold, evaporating substantially all of the solvent therefrom to form adry solid residue comprising said ductile metal with said saltassociated with the particles thereof, and subjecting said residue toheating in a dry reducing atmosphere at an elevated temperaturesufficient to decompose said salt to form a refractory oxide finelydispersed therethrough.

12. The method of claim 11 wherein the amount of refractoryoxide-forming salt wet mixed with the metal powder corresponds to about2% to 25% by volume of its corresponding refractory oxide taken on thedry basis of the metal powder mixture.

13. The method of claim 12 wherein the oxygen-containing salt is athorium salt which decomposes to thoria.

14. The method of claim 13 wherein the thorium salt is thorium nitrate,and wherein the amount of thorium nitrate present corresponds to about4% to 12% by volume of thoria taken on the dry basis of the metal powdermixture.

15. The method of claim 14 wherein the particle size of the ductilemetal powder ranges up to about 10 microns.

16. The method of claim 11 wherein the solid residue 9 10 isconsolidated into a hot workable compact and wherein 2,766,032 10/56Meister 75-206 said compact is hot extruded into a wrought metal shape.3,019,103 1/62 Alexander 75-206 3,069,759 12/62 Grant et a1 75-206 XReferences Cited by the Examiner UNITED STATES PATENTS 5 WHITMORE A.WILTZ, Primary Examiner.

2,757,446 8/56 Boegehold 29-4205 HYLAND BIZOT, Examiner.

1. A WET METHOD FOR PRODUCING A HOMOGENEOUS METALCONTAINING MIXTURE FORUSE IN THE PRODUCTION OF DISPERSION STRENGTHENED WROUGHT DUCTILE METALSOF MELTING POINT ABOVE 250*C. HAVING A UNIFORM DISPERSION THERETHROUGHOF A REFRACTORY OXIDE PHASE WHOSE NEGATIVE FREE ENERGY OF FORMATION ISAT LEAST ABOUT 100,000 CALORIES PER GRAM ATOM OF OXYGEN AT ABOUT 25*C.WHICH COMPRISES, PROVIDING A SOLUTION OF A SOLUBLE DECOMPOSABLEREFRACTORY OXIDE-FORMING SALT WITH A NON-RESIDUE LEAVING SOLVENT, SAIDSALT BEING ONE WHICH DECOMPOSES ON HEATING TO A REFRACTORY OXIDE WHOSENEGATIVE FREE ENERGY OF FORMATION IS AT LEAST ABOUT 100,000 CALORIES PERGRAM ATOM OF OXYGEN AT ABOUT 25*C., SLOWLY ADDING SAID FINELY DIVIDEDDUCTILE MATRIX METAL POWDER OF MELTING POINT ABOVE 250*C. TO SAIDSOLUTION WHILE RAPIDLY STIRRING AND EVAPORATING SAID SOLUTION TO PRODUCEA HIGHLY VISCOUS SLURRY WHICH TENDS TO RESIST FURTHER STIRRING,CONFINING THE HIGHLY VISCOUS SLURRY IN A MOLD, EVAPORATING SUBSTANTIALLYALL OF THE SOLVENT THEREFROM TO FORM A DRY SOLID RESIDUE COMPRISING SAIDDUCTILE METAL WITH SAID SALT ASSOCIATED WITH THE PARTICLES THEREOF, ANDSUBJECTING SAID RESIDUE TO HEATING IN A DRY REDUCING ATMOSPHERE AT ANELEVATED TEMPERATURE SUFFICIENT TO DECOMPOSE SAID SALT TO FORM AREFRACTORY OXIDE FINELY DISPERSED THERETHROUGH.